Combine harvesters are widely used in the harvesting of various types of grain, corn and other crops of which the seed is harvested. Typically, a combine harvester comprises a header having a cutter bar, which cuts the plants that contain the seeds to be harvested from the field. The thus harvested crop is threshed inside the combine harvester, in which process the seeds are separated from the other parts of the plants. The stalks of the harvested plants are removed from the combine harvester via a straw walker and a mixture of harvested seeds and by-products remains in the combine harvester. These by-products (e.g. chaff or “ears”) are generally smaller than the stalks that are removed from the combine harvester via the straw walker.
The mixture of harvested seeds and these by-products is transported to a cleaning system, in which the threshed seeds are separated from the by-products. The cleaning system generally comprises one or more grain pans and one or more sieves, which perform a reciprocating movement during use. The sieved seeds are then collected and transported to the grain tank of the combine harvester, which is generally emptied periodically.
The grain pan and sieve or sieves of the cleaning system are generally arranged at an angle relative to the horizontal, with the front end of the sieve (that is, the end closest to the cutter bar) lower than the rear end of the sieve. The reciprocating movement of the grain pan and sieve makes that the seeds and by-products are thrown upwards and backwards by the grain pan or sieve, respectively. A fan blows air over and through the sieve, to catch the lighter particles of the by-products and keep them airborne until they are blown out of the combine harvester.
In known arrangements, the combine harvester comprises a drive mechanism for the cleaning system. Such a drive mechanism typically comprises a rotatable drive shaft that drives the grain pan or grain pans as well as the sieve or sieves. The grain pans and sieves are connected to the rotatable drive shaft through a transmission comprising mechanical elements such as eccentric drives and linkages. Often, one linkage system is used to drive multiple sieves, grain pans or a sieve and a grain pan at the same time. For example, DE 2743733 uses such an arrangement.
In these known arrangements, the mechanical elements in the transmission are subjected to high mechanical loads.